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                    <h1>ES6编程风格摘要</h1>
                    
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                         作者 MillZhang
                        <span>
                          日期 2017-07-04
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                           title="es6">es6</a>
                        
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            ES6编程风格摘要
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                <h3 id="块级作用域"><a href="#块级作用域" class="headerlink" title="块级作用域"></a>块级作用域</h3><ul>
<li><p><code>let</code>取代<code>var</code></p>
</li>
<li><p>全局常量和线性安全</p>
</li>
</ul>
<blockquote>
<p>全局环境中,不应设置变量,只应设置常量,优先使用<code>const</code><br><code>const</code>定义的常量不可修改</p>
</blockquote>
<h3 id="字符串"><a href="#字符串" class="headerlink" title="字符串"></a>字符串</h3><blockquote>
<p>静态字符串一律使用单引号或反引号,不使用双引号.动态字符串,使用反引号.</p>
</blockquote>
<figure class="highlight js"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">const</span> a = <span class="string">'foo'</span>;</div><div class="line"><span class="keyword">const</span> b = <span class="string">`foo<span class="subst">$&#123;aaa&#125;</span>bar`</span>;</div></pre></td></tr></table></figure>
<h3 id="解构赋值"><a href="#解构赋值" class="headerlink" title="解构赋值"></a>解构赋值</h3><ul>
<li>使用数组成员对变量赋值时,优先使用解构赋值.</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">const</span> arr = [<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>];</div><div class="line"></div><div class="line"><span class="comment">// bad</span></div><div class="line"><span class="keyword">const</span> first = arr[<span class="number">0</span>];</div><div class="line"><span class="keyword">const</span> second = arr[<span class="number">1</span>];</div><div class="line"></div><div class="line"><span class="comment">// good</span></div><div class="line"><span class="keyword">const</span> [first, second] = arr;</div></pre></td></tr></table></figure>
<ul>
<li>函数的参数如果是对象的成员,优先使用解构赋值</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div></pre></td><td class="code"><pre><div class="line"><span class="comment">// bad</span></div><div class="line"><span class="function"><span class="keyword">function</span> <span class="title">getFullName</span>(<span class="params">user</span>) </span>&#123;</div><div class="line">  <span class="keyword">const</span> firstName = user.firstName;</div><div class="line">  <span class="keyword">const</span> lastName = user.lastName;</div><div class="line">&#125;</div><div class="line"></div><div class="line"><span class="comment">// good</span></div><div class="line"><span class="function"><span class="keyword">function</span> <span class="title">getFullName</span>(<span class="params">obj</span>) </span>&#123;</div><div class="line">  <span class="keyword">const</span> &#123; firstName, lastName &#125; = obj;</div><div class="line">&#125;</div><div class="line"></div><div class="line"><span class="comment">// best</span></div><div class="line"><span class="function"><span class="keyword">function</span> <span class="title">getFullName</span>(<span class="params">&#123; firstName, lastName &#125;</span>) </span>&#123;</div><div class="line">&#125;</div></pre></td></tr></table></figure>
<ul>
<li>如果函数返回多个值，优先使用对象的解构赋值，而不是数组的解构赋值。这样便于以后添加返回值，以及更改返回值的顺序。</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div></pre></td><td class="code"><pre><div class="line"><span class="comment">// bad</span></div><div class="line"><span class="function"><span class="keyword">function</span> <span class="title">processInput</span>(<span class="params">input</span>) </span>&#123;</div><div class="line">  <span class="keyword">return</span> [left, right, top, bottom];</div><div class="line">&#125;</div><div class="line"></div><div class="line"><span class="comment">// good</span></div><div class="line"><span class="function"><span class="keyword">function</span> <span class="title">processInput</span>(<span class="params">input</span>) </span>&#123;</div><div class="line">  <span class="keyword">return</span> &#123; left, right, top, bottom &#125;;</div><div class="line">&#125;</div><div class="line"></div><div class="line"><span class="keyword">const</span> &#123; left, right &#125; = processInput(input);</div></pre></td></tr></table></figure>
<h3 id="对象"><a href="#对象" class="headerlink" title="对象"></a>对象</h3><ul>
<li>单行定义的对象,最后一个成员不以逗号结尾.多行定义的对象,最后一个成员以逗号结尾.</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div></pre></td><td class="code"><pre><div class="line"><span class="comment">// bad</span></div><div class="line"><span class="keyword">const</span> a = &#123; <span class="attr">k1</span>: v1, <span class="attr">k2</span>: v2, &#125;;</div><div class="line"><span class="keyword">const</span> b = &#123;</div><div class="line">  <span class="attr">k1</span>: v1,</div><div class="line">  <span class="attr">k2</span>: v2</div><div class="line">&#125;;</div><div class="line"></div><div class="line"><span class="comment">// good</span></div><div class="line"><span class="keyword">const</span> a = &#123; <span class="attr">k1</span>: v1, <span class="attr">k2</span>: v2 &#125;;</div><div class="line"><span class="keyword">const</span> b = &#123;</div><div class="line">  <span class="attr">k1</span>: v1,</div><div class="line">  <span class="attr">k2</span>: v2,</div><div class="line">&#125;;</div></pre></td></tr></table></figure>
<ul>
<li>对象尽量静态化，一旦定义，就不得随意添加新的属性。如果添加属性不可避免，要使用<code>buObject.assign</code>方法。</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div></pre></td><td class="code"><pre><div class="line"><span class="comment">// bad</span></div><div class="line"><span class="keyword">const</span> a = &#123;&#125;;</div><div class="line">a.x = <span class="number">3</span>;</div><div class="line"></div><div class="line"><span class="comment">// if reshape unavoidable</span></div><div class="line"><span class="keyword">const</span> a = &#123;&#125;;</div><div class="line"><span class="built_in">Object</span>.assign(a, &#123; <span class="attr">x</span>: <span class="number">3</span> &#125;);</div><div class="line"></div><div class="line"><span class="comment">// good</span></div><div class="line"><span class="keyword">const</span> a = &#123; <span class="attr">x</span>: <span class="literal">null</span> &#125;;</div><div class="line">a.x = <span class="number">3</span>;</div></pre></td></tr></table></figure>
<h3 id="数组"><a href="#数组" class="headerlink" title="数组"></a>数组</h3><ul>
<li>使用扩展运算符(…)拷贝数组</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div></pre></td><td class="code"><pre><div class="line"><span class="comment">// bad</span></div><div class="line"><span class="keyword">const</span> len = items.length;</div><div class="line"><span class="keyword">const</span> itemsCopy = [];</div><div class="line"><span class="keyword">let</span> i;</div><div class="line"></div><div class="line"><span class="keyword">for</span> (i = <span class="number">0</span>; i &lt; len; i++) &#123;</div><div class="line">  itemsCopy[i] = items[i];</div><div class="line">&#125;</div><div class="line"></div><div class="line"><span class="comment">// good</span></div><div class="line"><span class="keyword">const</span> itemsCopy = [...items];</div></pre></td></tr></table></figure>
<ul>
<li>使用<code>Array.from</code>方法,将类似数组的对象转为数组</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">const</span> foo = <span class="built_in">document</span>.querySelectorAll(<span class="string">'.foo'</span>);</div><div class="line"><span class="keyword">const</span> nodes = <span class="built_in">Array</span>.from(foo);</div></pre></td></tr></table></figure>
<ul>
<li>数组遍历可以使用<code>for-of</code></li>
</ul>
<h3 id="函数"><a href="#函数" class="headerlink" title="函数"></a>函数</h3><ul>
<li>立即执行函数可以写成箭头函数的形式</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div></pre></td><td class="code"><pre><div class="line">(<span class="function"><span class="params">()</span>=&gt;</span>&#123;</div><div class="line">    <span class="built_in">console</span>.log(<span class="string">`....`</span>)</div><div class="line">&#125;)();</div></pre></td></tr></table></figure>
<ul>
<li>那些需要使用函数表达式的场合，尽量用箭头函数代替。因为这样更简洁，而且绑定了<code>this</code>。</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div></pre></td><td class="code"><pre><div class="line"><span class="comment">// bad</span></div><div class="line">[<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>].map(<span class="function"><span class="keyword">function</span> (<span class="params">x</span>) </span>&#123;</div><div class="line">  <span class="keyword">return</span> x * x;</div><div class="line">&#125;);</div><div class="line"></div><div class="line"><span class="comment">// good</span></div><div class="line">[<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>].map(<span class="function">(<span class="params">x</span>) =&gt;</span> &#123;</div><div class="line">  <span class="keyword">return</span> x * x;</div><div class="line">&#125;);</div><div class="line"></div><div class="line"><span class="comment">// best</span></div><div class="line">[<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>].map(<span class="function"><span class="params">x</span> =&gt;</span> x * x);</div></pre></td></tr></table></figure>

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                    <ol class="toc"><li class="toc-item toc-level-3"><a class="toc-link" href="#块级作用域"><span class="toc-text">块级作用域</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#字符串"><span class="toc-text">字符串</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#解构赋值"><span class="toc-text">解构赋值</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#对象"><span class="toc-text">对象</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#数组"><span class="toc-text">数组</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#函数"><span class="toc-text">函数</span></a></li></ol>
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